With the increasingly large scale of integration of semiconductor devices, the space for forming capacitors is decreasing. Therefore, intense research efforts have been directed toward assuring sufficient capacitance in the space available.
The capacitance of a capacitor is determined by the area of the electrodes, the dielectric constant of a dielectric layer, and the distance between electrodes. Accordingly, in order to increase the capacitance, methods of increasing the effective area of a capacitor, of decreasing the thickness of a dielectric layer between two electrodes, and of replacing the dielectric layer with a material having a high dielectric constant have been intensively and extensively studied.
The method of increasing the effective area takes chip real estate away from other devices, due to the high degree of integration and miniaturization. A better solution is to increase the capacitance through optimizing the layering process. However, it becomes difficult to deposit the upper film and the structure becomes complicated, thereby resulting in a difficult manufacturing process. Further, when the dielectric constant is increased or the thickness of the dielectric layer is decreased, leakage current may be increased and faulty devices may result from electrical breakdown or the like.